1. Field of the Invention
This invention relates to a dental impression tray especially adapted for use with impression materials that cure upon exposure to light.
2. Description of the Related Art
Dental impression trays are used to hold impression material for making a model of a patient's tooth and oral tissue anatomy so that a crown, bridge, denture, veneer, restoration or the like can be made. A typical procedure involves placing a quantity of impression material in an open trough or channel of the tray and then pressing the tray onto the dental arch of the patient. The impression material is allowed to cure while in the oral cavity. The tray with the impression material is then removed from the oral cavity, and the impression material is used to prepare a positive model that replicates the selected area of the patient's arch.
Most conventional dental impression materials are made by mixing two components immediately before the impression is taken. Mixing of the components initiates a polymerization reaction that eventually causes the material to harden and cure. Consequently, as soon as the components are mixed, it is important for the dental practitioner to promptly deliver the tray to the oral cavity and accurately position the impression material relative to the selected area of the dental arch so that an accurate impression can be made.
Typically, a manufacturer of dental impression material provides recommended guidelines to the practitioner that specify both a working time and a setting point time to be followed when using the material. The working time is determined by the composition of the polymeric system and is the total time allowed for mixing the components, placing the mixed components in the tray, delivering the tray to the oral cavity and accurately seating the impression material onto desired areas of the patient's dental arch. The setting point time relates to the degree of curing of the impression material, and represents the total time that should elapse (after the components are mixed) before the tray is removed from the oral cavity in order to ensure that the impression material has cured to a degree sufficient that the impression will not be distorted as the tray is removed from contact with the dental arch.
A variety of dental impression materials are currently available that polymerize upon mixing of two components. Such materials include, for example, hydrocolloids, polysulfides, polyethers and silicones. Recommended working times and setting point times for such materials are often in the range of about 1.25 to 7 minutes and 1.5 to 10 minutes respectively.
Unfortunately, dental impression materials that begin to polymerize upon mixing are not entirely satisfactory, in that taking of the impression should be completed within a predetermined amount of time. If, for example, the procedure is interrupted by the dentist or by the patient for some unforeseen reason, the impression material may cure to such a degree that it is unusable before the procedure can be resumed. Another problem associated with such impression materials relates to the differences in recommended working times and setting point times for the variety of materials that are currently available, since a dental practitioner who has long used one type of material may fail to follow the manufacturer's recommended working time and setting point time for another material that is substituted.
In many impression materials that cure upon mixing, the length of the working time and the setting point time are determined by the amount of catalyst in the mixture. As a consequence, one who attempts to decrease the setting point time by increasing the catalyst concentration may be frustrated because the working time may also be unduly shortened. Conversely, an attempt to increase the working time may result in lengthening the setting point time by an unsatisfactory amount.
Certain impression materials that are mixed in the dental office are also unsatisfactory in instances where the mixing method (such as hand spatulation) introduces air bubbles into the mixture. Air bubbles may cause surface imperfections in the finished impression. In addition, it should be noted that mixing of the materials by hand spatulation is inherently somewhat time consuming.
It has been suggested that the use of photopolymerizable dental impression materials overcomes the disadvantages often associated with impression materials that are curable when mixed. Photopolymerizable impression materials include a photocatalyst and/or a photoinitiator that initiates polymerization of the impression material upon exposure to an appropriate wavelength of light. In the absence of such a light source, the impression material will remain substantially unpolymerized for a relatively long period of time so that the dental practitioner can ensure that the tray is accurately positioned before the impression material cures. Examples of photocurable materials are set out in U.S. Pat. Nos. 5,179,186, 5,145,886, 4,761,136, 4,543,063 and 4,740,159 and European patent applications publication nos. 0460478, 0269071, 0255286, 0173085 and 0170219.
Photopolymerizable impression materials also provide a potential advantage in instances where the tray is accurately placed in the mouth in a relatively short amount of time. In such instances, the light source can be immediately activated to begin curing of the impression material, so that the overall time necessary to complete the impressioning procedure can be reduced. By contrast, a practitioner using an impression material that immediately begins to cure upon mixing is generally unable to shorten the time necessary for completion of the impressioning procedure even when the tray is quickly placed in the oral cavity because polymerization reaction will proceed at the same rate.
However, known dental impression trays and procedures for using such trays with photopolymerizable dental impression materials are generally unsatisfactory. Some practitioners have attempted to use photopolymerizable impression material by placing the material in a transparent tray and directing a source of light through the tray and into the impression material to initiate polymerization. Such a procedure is described, for example, in U.S. Pat. No. 4,867,682.
In the past, the light source suggested for use in curing photocurable impression materials is often the same dental material curing apparatus that is commonly found in dental offices for curing adhesives, sealants and restorative materials. Such curing apparatus are described, for example, in U.S. Pat. Nos. 4,888,489 and 5,147,204 (both of which are assigned to the assignee of the present invention) and have a rigid light guide made of a bundle of optical fibers that are fused together. Unfortunately, it is difficult to use such a light guide in the oral cavity when a dental impression tray is also in place in the oral cavity, since space in the oral cavity is somewhat limited and the patient may experience discomfort in an attempt to open his or her jaws to an extent sufficient to enable the light guide to be positioned next to various regions of the tray. The practitioner should also take care to avoid bumping the tray with the light guide so that the impression is not distorted. Another disadvantage with such practice is that the hand-held light source may not be directed toward all regions of the tray, resulting in a failure of the impression material to cure in such regions.
U.S. Pat. Nos. 4,553,936 and 4,790,752 describe dental impression trays having a portal or socket for detachably receiving the light guide of dental material curing apparatus. The trays in certain embodiments of these patents have reflective surfaces or other structure to facilitate directing the light to various regions of the tray. However, such trays are disadvantageous in that the light source is relatively expensive and the light guide must be sterilized along with the tray between uses.
Another problem associated with prior methods and devices for curing photocurable impression material involves the amount of useful light energy available from conventional light sources and the resultant time necessary to obtain the satisfactory cure. It has been observed that curing times using photocurable dental impression material and conventional light sources are often relatively lengthy, resulting in a nuisance and expense to both the dental practitioner and the patient. Such relatively lengthy curing times may be due to the variation in intensity of the light that reaches various regions of the tray. In addition, incandescent lamps emit light over a broad range of wavelengths, much of which is wasted since it is not absorbed by the photoinitiator or photocatalyst.